John D. B. Featherstone

Demineralization and remineralization around orthodontic appliances: An in vivo study

The presence of clinically detectable areas of decalcification (observable as whitened areas) following the removal of orthodontic appliances is well recognized. The aim of the present study was to determine quantitatively the amount of demineralization and the ability of commercially available products to inhibit or reverse orthodontically related demineralization. Twenty orthodontic patients scheduled to have premolars extracted were randomly divided into four groups--one control and three test groups. The extracted premolars (numbering 58) were bracketed using an acid-etch composite system; each patient was given precise oral hygiene instructions and supplied with a sodium fluoride (1,100 ppm fluoride) dentifrice and an orthodontic toothbrush. The control group brushed only with the supplied dentifrice. In addition to brushing with the dentifrice, those in test group I rinsed once each night with a sodium fluoride (0.05%) mouthrinse; group II received a weekly topical APF treatment (1.2% fluoride); and Group III received a weekly topical APF treatment and rinsed once each night with the sodium fluoride mouthrinse. All premolars were extracted after 1 calendar month. Mineral profiles were determined on cross-sectioned teeth 50 to 75 micron occlusal and cervical to the brackets, directly underneath the brackets, and 500 micron away from the brackets. The control teeth (dentifrice only) demonstrated up to 15% demineralization to a depth of 50 micron. All of the test teeth produced rehardening and/or inhibition of demineralization (P less than 0.01). Those in test group III showed a particularly hard outer layer. The study demonstrated that measurable demineralization occurred around orthodontic appliances after only 1 month and this demineralization can be completely inhibited and/or reversed by the use of commercially available fluoride products.

The Continuum of Dental Caries—Evidence for a Dynamic Disease Process

The eventual outcome of dental caries is determined by the dynamic balance between pathological factors that lead to demineralization and protective factors that lead to remineralization. Pathological factors include acidogenic bacteria, inhibition of salivary function, and frequency of ingestion of fermentable carbohydrates. Protective factors include salivary flow, numerous salivary components, antibacterials (both natural and applied), fluoride from extrinsic sources, and selected dietary components. Intervention in the caries process can occur at any stage, either naturally or by the insertion of some procedure or treatment. Dental caries covers the continuum from the first atomic level of demineralization, through the initial enamel or root lesion, through dentinal involvement, to eventual cavitation. The dynamic balance between demineralization and remineralization determines the end result. The disease is reversible, if detected early enough. Since demineralization can be quantified at early stages, before frank cavitation, intervention methods can be tested by short-term clinical trials.

Imaging caries lesions and lesion progression with polarization sensitive optical coherence tomography

New diagnostic tools are needed for the characterization of dental caries in the early stages of development. If carious lesions are detected early enough, they can be arrested without the need for surgical intervention. The objective of this study was to demonstrate that polarization sensitive optical coherence tomography (PS-OCT) can be used for the imaging of early caries lesions and for the monitoring of lesion progression over time. High-resolution polarization resolved images were acquired of natural caries lesions and simulated caries lesions of varying severity created over time periods of 1 to 14 days. Linearly polarized light was incident on the tooth samples and the reflected intensity in both orthogonal polarizations was measured. PS-OCT was invaluable for removing the confounding influence of surface reflections and native birefringence necessary for the enhanced resolution of the surface structure of caries lesions. This study demonstrated that PS-OCT is well suited for the imaging of interproximal and occlusal caries, early root caries, and for imaging decay under composite fillings. Longitudinal measurements of the reflected light intensity in the orthogonal polarization state from the area of simulated caries lesions linearly correlated with the square root of time of demineralization indicating that PS-OCT is well suited for monitoring changes in enamel mineralization over time.

NATURE OF LIGHT SCATTERING IN DENTAL ENAMEL AND DENTIN AT VISIBLE AND NEAR-INFRARED WAVELENGTHS

The light-scattering properties of dental enamel and dentin were measured at 543, 632, and 1053 nm. Angularly resolved scattering distributions for these materials were measured from 0° to 180° using a rotating goniometer. Surface scattering was minimized by immersing the samples in an index-matching bath. The scattering and absorption coefficients and the scattering phase function were deduced by comparing the measured scattering data with angularly resolved Monte Carlo light-scattering simulations. Enamel and dentin were best represented by a linear combination of a highly forward-peaked Henyey-Greenstein (HG) phase function and an isotropic phase function. Enamel weakly scatters light between 543 nm and 1.06 µm, with the scattering coefficient (µ(s)) ranging from µ(s) = 15 to 105 cm(-1). The phase function is a combination of a HG function with g = 0.96 and a 30-60% isotropic phase function. For enamel, absorption is negligible. Dentin scatters strongly in the visible and near IR (µ(s)≅260 cm(-1)) and absorbs weakly (µ(a) ≅ 4 cm(-1)). The scattering phase function for dentin is described by a HG function with g = 0.93 and a very weak isotropic scattering component (˜ 2%).

Mechanistic Aspects of the Interactions Between Fluoride and Dental Enamel

For many years after the discovery of its caries preventive effect, fluoride was thought to be primarily active by lowering the solubility of the apatitic mineral phase of the dental hard tissues. Recent findings have shed new light on the mechanisms by which fluoride inhibits or delays dental caries. Fluoride present in the oral fluids alters the rate of the naturally occurring dissolution and reprecipitation processes at the tooth-oral fluid interface. Demineralization of enamel is inhibited by concentrations of fluoride in the sub-ppm range. Likewise, remineralization of incipient caries lesions (the earliest stage of enamel caries) is accelerated by trace amounts of fluoride. As these two processes comprise dental caries the physiological balance between hard tissue breakdown and repair is favorably shifted by fluoride. The driving force for both phenomena is thermodynamic, that is, fluorapatite or a fluoridated hydroxyapatite may form when fluoride is supplied at low concentrations. This article critically reviews the current information about tooth-fluoride interactions, both from laboratory and clinical studies.

Fluoride Varnish Efficacy in Preventing Early Childhood Caries

To determine the efficacy of fluoride varnish (5% NaF, Duraphat®, Colgate) added to caregiver counseling to prevent early childhood caries, we conducted a two-year randomized, dental-examiner-masked clinical trial. Initially, 376 caries-free children, from low-income Chinese or Hispanic San Francisco families, were enrolled (mean age ± standard deviation, 1.8 ± 0.6 yrs). All families received counseling, and children were randomized to the following groups: no fluoride varnish, fluoride varnish once/year, or fluoride varnish twice/year. An unexpected protocol deviation resulted in some children receiving less active fluoride varnish than assigned. Intent-to-treat analyses showed a fluoride varnish protective effect in caries incidence, p < 0.01. Analyzing the number of actual, active fluoride varnish applications received resulted in a dose-response effect, p < 0.01. Caries incidence was higher for ‘counseling only’ vs. ‘counseling + fluoride varnish assigned once/year’ (OR = 2.20, 95% CI 1.19–4.08) and ‘twice/year’ (OR = 3.77, 95% CI 1.88–7.58). No related adverse events were reported. Fluoride varnish added to caregiver counseling is efficacious in reducing early childhood caries incidence.

Laser Effects On Dental Hard Tissues

The use of lasers in dentistry has been considered for over 20 years. Higher-energy density lasers were shown to fuse enamel but were potentially unsafe. Subsequently, low-energy density laser radiation was shown to affect artificial caries lesion formation. Recent studies have shown that carbon dioxide lasers can successfully be used at low-energy densities to fuse enamel, dentin, and apatite. Our studies have shown that specific wavelengths are highly efficient. These wavelengths are directly related to the infrared absorption regions of apatite. We have conducted studies with enamel and dentin, using pulsed CO2 laser radiation in the 9.32-μm to 10.49-μm region with energy densities in the 10 to 50 J.cm-2 range. This laser treatment caused surface fusion and inhibition of subsequent lesion progression and markedly improved the bonding strength of a composite resin to dentin. Similar studies have shown no pulpal damage or permanent deleterious effect on soft tissues. This improved understanding of the scientific rationale for the interaction of CO2 lasers with teeth can lead to several clinical applications. This will depend, however, on the development of a technology to direct a specific frequency laser beam precisely to a desired site.

Understanding the Chemistry of Dental Erosion

The mineral in our teeth is composed of a calcium-deficient carbonated hydroxyapatite (Ca10-xNax(PO4)6-y(CO3)z(OH)2-uFu). These substitutions in the mineral crystal lattice, especially carbonate, renders tooth mineral more acid soluble than hydroxyapatite. During erosion by acid and/or chelators, these agents interact with the surface of the mineral crystals, but only after they diffuse through the plaque, the pellicle, and the protein/lipid coating of the individual crystals themselves. The effect of direct attack by the hydrogen ion is to combine with the carbonate and/or phosphate releasing all of the ions from that region of the crystal surface leading to direct surface etching. Acids such as citric acid have a more complex interaction. In water they exist as a mixture of hydrogen ions, acid anions (e.g. citrate) and undissociated acid molecules, with the amounts of each determined by the acid dissociation constant (pKa) and the pH of the solution. Above the effect of the hydrogen ion, the citrate ion can complex with calcium also removing it from the crystal surface and/or from saliva. Values of the strength of acid (pKa) and for the anion-calcium interaction and the mechanisms of interaction with the tooth mineral on the surface and underneath are described in detail.

MORPHOLOGY, HISTOLOGY AND CRYSTALLOGRAPHY OF HUMAN DENTAL ENAMEL TREATED WITH PULSED LOW-ENERGY INFRARED-LASER RADIATION

The surface morphology of human enamel treated with pulsed, infrared laser radiation was examined using reflected light and scanning electron microscopy. Thin (

An Infrared Method for Quantification of Carbonate in Carbonated Apatites

Carbonated apatites of known carbonate content were used to develop a method which uses infrared (IR) spectroscopy for quantitative estimation of carbonate. The ratio of the extinction of the IR carbonate band at about 1,415 cm––1 to the extinction of the phosphate band at about 575 cm––1 is linearly related to the carbonate content of the carbonated apatite. Mixtures of BaCO3 and commercially available hydroxyapatite or tricalcium phosphate are used to standardize the apparatus. The method allows carbonate estimation to better than ± 10% in the range 1–12% wt/wt.